1. Field of the Invention
The present invention relates to the processing method of a video image or the like, and more particularly relates to an image still area determination device for determining the still area of each block or the like when converting an interlace scan type field image into a progressive scan type frame image or the like.
2. Description of the Related Art
For example, in a video signal processing device, it is important in efficient signal processing to determine still areas between consecutive frames. For example, it is important to determine still areas in order to prevent the flicker and blur of an image when converting an interlace scan type field image into a progressive scan type frame image.
The prior art of this still area determination method is described below with reference to FIGS. 1 and 2. FIG. 1 shows the configuration of the conventional image still area determination device. The determination device shown in FIG. 1 comprises a pixel value difference extraction unit 100 for calculating the pixel value difference between the corresponding pixels of two frame images when the current frame image and a frame image immediately before it are inputted, a block averaging unit 101 for averaging the pixel value differences of the pixels of each block and a block stillness determination unit 102 for determining the stillness of a block, comparing the output of the block averaging unit 101 with a predetermined threshold value.
FIG. 2 explains the still area determining operation for each block of the image still area determination device shown in FIG. 1. This still area determination process is applied to the block composed of 2×2 pixels enclosed by a solid line in the center of FIG. 2, of each of the current frame image and a frame image immediately before it. However, when determining block stillness between pixel blocks each composed of 2×2 pixels, the pixel value difference extraction unit 100 calculates the pixel value difference between each pair of corresponding pixels in a square area with 4×4 pixels including one pixel around the block (enclosed by a dotted line), of the current frame image and the frame image immediately before it. Then, the block averaging unit 101 calculates the average value of the 16 difference values and provides the block stillness determination unit 102 with the value as an average value of the block composed of 2×2 pixels. If this value is smaller than the threshold value, the block is determined to be a still area, and a signal for the determination result is outputted.
However, as described with reference to FIG. 2, in such a conventional method, since a pixel value difference is calculated between directly corresponding pixels, even a small imperceptible movement causes a difference between pixel values, and as a result, sometimes a block which should be determined to be still area is not determined so. In such a case, for example, flicker occurs in a progressive scan type frame image converted from an interlace scan type field image.
In one of such conventional methods of detecting a still area in an image (for example, Patent reference 1), for example, a reliable still area detection algorithm for calculating a pixel value difference between corresponding pixels of consecutive frames, deleting an isolated still area or adjacent small blocks of still areas on a temporary map of a still area which are generated by accumulating pixel value differences of each block, based on the calculated value in order to calculate the final map of an still area is disclosed.
However, even in Patent reference 1, since a pixel value difference is calculated between directly corresponding pixels of consecutive frames, a pixel value difference caused by a small image movement affects the determination of a still area and its image signal processing causes flicker and blur.
Patent reference 1: Japanese laid-open disclosure public patent bulletin No. 2000-78533